Process for obtaining coal particularly poor in ash content



?atentcd May 22, 1945 PROCESS FOR. OBTAINING COAL PARTICU- LARLY POOR IN ASH CONTENT Friedrich Ludwig Kiihlwein, Essen, Germany; vested in the Alien Property Custodian No Drawing. Application January 9, 1941, Serial No. 373,832. In Germany December 18, 1939 1 Claim.

This invention relates to a process for obtaining coal particularly poor in ash content as required in increasing degree for various industrial purposes, especially a starting material in the production of electrodes.

The efforts made to reduce the ash content of coal to the maximum admissible for these purposes have not been completely successful till now. The usual methods according to which the coal is prepared without considering the different primary ash contents of its structural constituents may be disregarded from the outset, since the application of such methods results at best in ash contents of several percents, even if a very low yield is accepted, whereas the maximum permissible ash content of coal suited for the purposes stated must be far below 1 It is therefore necessary to carry on the preparation along petrographic principles applying particularly to coal, which involves the elimination of those structural constituents oi the coal that disclose per se a materially higher combined ash content, such as fusite containing the secondary epigenetic mineral substance,.chiefiy pyrite and calcite, and durite containing the secondary epigenetic clay substance, so as to effect an enrichment of the remaining vitrite and clarite portions which contain merely the primary plant ashes. 7 Various preparation methods have been proposed tor this purpose, as the application of the elastic impact for separating the structural constituents, the preparation in liquids possessing high specific gravity, and some flotation processes having a selective eflect with respect to the petrography of coal.

All these proposals fail, however, to bring about a sufilcient enrichment of vitrite and clarite so as to obtain the desired low ash content.

It is the object of the invention to provide a process for obtaining coal particularly poor in ash content, which satisfies both technical and economic requirements, and this object is attained by subjecting coal of suitable grain size, possibly in the form of a washed tine grained product, first to one of the known preparation methods relying for instance on treatment in liquids of high specific gravity, trough washing .or electrostatic processing, which at least to a certain extent have a petrographieally separating eflfect, and then causing the refined coal obtained by this preparation and having already a very low ash content amounting to less than 2% to undergo ordinary flotation, possibly after it has previously been disintegrated if necessary to acquire a grain size required for the complete separation of the structural constituents. The flotation has also a petrographically dissociating effect, since due to the preceding steps of treatment, particularly to disintegration, mineral substance has been superficially exposed on the structural constituents of higher combined ash content, so that they are wettedby water during flotation and do not float up. It has been found that in this way a virtrite-clarite enrichment of approximately with an ash content of below 0.6% can be obtained.

In carrying out the method according to the present invention the first step is to produce coal of a suitable small grain size. This may be done by known methods, such as grinding,and the resulting product should be sufficiently fine to permit separation of the durite and fusite grains from the vitrite and clarite grains in the subsequent steps. The next step consists in the elimination from this coal of the structural constituents thereof having a mineral ash content materially higher than desired, such as fusite and durite, thereby effecting an enrichment oi the plant-ash containing substances such as vitrite and clarite. This step of the process may also be carried out by known methods. For example, the so-called heavy fluid processes may be used. In these, the density or a liquid is so adJusted that the durite and fusite particles suspended therein and which have high specific gravity because of the higher proportion of combined ash therein, will be caused to sink, whereas the vitrite and clarite particles, being lighter, will float. to the top or the liquid where they may be gathered. An scribed in detail in Gluckaut 1941, No. 6, pages 93 101 and No. "I, pages 109-415. Other processes which may be used to eflect the preliminary separation required in the second step or the process are the so-called trough washing and electro-static processes. The trough washing process is described in Gluckauf 1938, No. 52, page 1117. The electro-static process is described in Gluckauf 1941, No. 5, pages 60-80. These processes are all well-known and no further description thereof will be given here.

After the preliminary separation eflected by the described second step of the process the refined" coal so obtained may, if desired, be disintegrated iurther, as by grinding. In the last step of the process the refined coal obtained from the preliminary separation step, and which may or may not have been subsequently ground, is subjected to a minerals-separation flotation process such as is well-known in the art, in which only usual and normal collecting and frothing agents are used in usual and well-known apparatus. The treatment of the coal in this step of the process causes the vitrite and clarite constituents to float to the top and collect there under the influence of the collecting and frothing agents.

The following examples presented to indicate the application of this invention are merely illustrative and not limitative in character:

EXAMPLE 1 Preparation of a washed fine coal first in a liquid of high specific gravity (step 1) and then by flotation of the refined coal obtained (step 2) From the washed fine coal representing the starting product and having an ash content of 3.2% a refined coal of 1.35% ash content at a vitrite-clariteenrichment of 81% is obtained due to preparation in a liquid of high specific gravity and particularly to the separation of bituminous hale. By subsequent flotation the ash content of the product is reduced to less than 0.6% and simultaneously the vitrite-clarite content increased to 94%. All structural constituents of high primary ash content, as durite, semifusinite 9,570,709 example or such a process one and fusinite, are therefore eliminated with the exception of unimportant residual quantities.

M 2 Preparation of an unwashed fine coal taken from a specimen cut out of a bed in a liquid of Mali. specific gravity (step 1) followed by flotation of the refined coal obtained (step 2) First stop Second mp Stu-tin Refined Pure coal cool cool In this instance, due to the preparation in a liquid of high specific gravity, the ash content of the refined coal amounts to 1.3% at a vitriteclarite enrichment of 89.5%. Subsequent flotation of the product yielded a pure coal with an ash content ofonly 0.45% and comprising 97.5% vitrite-clarite, because the original 9% contaminating structural constituents, as durite,

. semifusinite and fusinite exposed by intermediate disintegration, could be reduced to 2.5%. Compared with the values obtainable by known processes, a yield of 50% pure coal from washed coal or 40% from raw coal, notwithstanding the consideraby higher degree of purity, is remarkably high and clearly indicates the superiority of the new process. Furthermore, the process according to the invention is advantageous also for a subsequent chemical treatment of the concentrates obtained for the purpose of removing additional ash constituents, since the remaining slight ash content, owing to the resulting composition of the mineral substance, is present in an easily decomposable form.

What is claimed is:

That method of obtaining pure coal especially low in ash content which consists in reducing the coal to small grain size, separation of the reduced coal in heavy liquid to liberate such resiclues as shales, durite and fusite, the density of said liquid being adjusted to give a coal product enriched in vitrite-clarite and containing less than two percent ash, further disintegrating the coal product to completely separate the structural constituents, and subsequently subjecting the disintegrated partially enriched coal to froth flotation to produce a product having lessthan one percent ash and with further vitrite-clarite enrichment.

FRIEDRICH LUDWIG KUHLWEIN. 

